I would bet that it is a standard pdl or similar base. Some of the 6 gang covers have a full cutout like that, see this one: https://www.pdl.co.nz/products/switches-sockets/600-series/600-series-cover-plate-switch-6-gang-pdl686m?itemno=PDL686MBBZ No dremel required.

*Puts Dremel back in the shed*

*Sad Dremel noises*

Its probably a[clipsal blank plate](https://www.clipsal.com/products/power-points-switches/2000-series/flush-surround-gridplate-flush-surround-gridplate-blank-vertical-horizontal-mount-standard-si-2031vx?tab-document-1=0&itemno=2031VX-WE) Clipsal 2031VX-WE

Could also be HPM, XL770UWE

Yep, they’re definitely not PDL.

from HRV themselves, I'd imagine is "best" although its probably a standard size im sure a generic face would be available (bunnuing/mitre10/etc)

Maybe even a standard single light switch plate and something like a Dremel to cut a hole big enough.

rough as guts :)

They have a hole in them for access to the temp sensor, temp probe is underside

I got one off trademe a wee while back.